The present invention relates to the art of wet-shaving and, in particular, is concerned with manufacturing a shaving unit, such as a disposable razor or a cartridge, by molding a thermoplastic material around the blade (or blades) so that the edge is protected during molding and exposed for shaving in the final product. Injection of a thermoplastic material around prefixed plastic or non-plastic parts to provide a composite article having a desired geometry can be referred as to insert molding.
Currently, wet-shaving units, such as disposable razors and cartridges, form a substantial portion of the demand of wet-shaving market.
With the exception of the blade or blades (and possibly a spacer) these units have been made out of thermoplastic material. The cap and blade support or seat components, depending upon the ultimate design, are molded separately and then assembled. For example the "MicroTrac" disposable razor manufactured by Gillette holds a single unit blade seat, back and cap, with the cap including outwardly extending fingers. The blade subassembly, consisting of two blades and a spacer, is inserted between the molded cap and seat with the finger-like projections extending from the top of the cap serving as leaf springs to retain the blade subassembly. This combination is then mated to a handle by press fitting into the blade subassembly. It is apparent that this process involves not only separate steps, but separate work stations requiring individual subassembly and ultimate assembly.
Other assembly processes for shaving units utilize projections extending either from the cap or the seat, which mate with openings in the opposing part and position the blades and/or spacer. The handle is usually made separately from the seat portion. Again, separate assembly steps at separate locations are required to produce the disposable razor.
A significant problem occasioned in the manufacture of wet-shaving units is the difficulty in establishing a reproducible shave geometry which provides optimum blade edge performance. Shave geometry relates to the spatial relationship, e.g., distance, angles(s), etc., of the surface(s) and blade edge(s) as they come into contact with the skin. Inherently, separate fabrication and assembly required to produce wet-shaving units detracts from the ability t precisely reproduce a selected shave geometry. Manufacturing such units also requires continuous vigilance to ensure quality control. Usually such vigilance translates into increased cost of production which results from additional labor.
Furthermore, blade edge performance relates to the response of the blade edge to forces imparted to it during shaving. Undue or uncontrolled vibration of the blade as it is drawn across the skin, sometimes referred to as "chatter," has been blamed by some experts as detracting from the feel of the shave and causing injury to the user. Separate fabrication and assembly required in known methods of manufacturing wet-shaving units are inimical to reducing "chatter" during shaving. Even minor tolerances built into mating parts for assembly will contribute to "chatter."
Consistently reproducible shave geometry has been improved to a certain extent by use of molded plastic parts having consistent dimensions. Quality assurance, however, still requires constant monitoring of production to ensure fabrication and assembly of parts are consistent. Overall blade edge performance has not been significantly improved by mere use of molded plastic parts.
Presently, there are no known hard and fast technical theories with respect to blade edge performance, but certain design characteristics are believed to enhance performance of wet-shaving units. Constant shave geometry whereby the spatial relationship of the skin-engaging portions, the seat, the cap, and the blade, are maintained over the entire length of the blade is certainly very important. In most cases, the blade over which constant shave geometry need be maintained is in a flat configuration with the edge having the profile of a straight line, although some artisans also recommend that the blade have a crown in the central portion for optimum shave feel. More recently, the discovery by the owners of the present technology of a flexible wet-shaving unit which deflects in response to forces imparted during shaving has required that shave geometry be maintained over the length of a blade which experiences a changing profile.
Regardless of the selected blade profile, it is substantially universally agreed that, in addition to maintenance of shave geometry, the blade edge should not be distorted from the edge profile, whether it is rigid or flexible. In the case of a flexible cartridge, although the entire cartridge body bends in response to forces during shaving (i.e., has a changing profile), the blade(s) should not deviate out of the fixed geometry of the shaving unit. Such blade distortion can easily result from several manufacturing difficulties. For example, care must be given to carefully matching mating parts during assembly of shaving units. Again, such care generally requires labor intensive quality assurance measures.
Vibration of the blade results from several structural features. One kind of vibration can be described as a "clam-shelling" affect of the subassembly components vibrating with respect to each other. Another vibration is that of the subassembly moving as a single component of the total razor unit. The cantilever configuration of the blade (and/or the blade subassembly) extending from its point of securement toward the unsupported edge contributes to this undesirable vibration. The inherent looseness of components in assembled wet-shaving units is yet another source of vibration. It is desirable, therefore, to minimize or eliminate one or more of the causes of vibration.
Still another source of vibration is caused by the blade engaging hair growing out of the skin surface. Recovery time of the blade should be minimized. This quick recovery may be characterized as stiffness.
In order to cure these problems, a disposable razor which could be assembled at a single work station having all the plastic parts assembled at one time or produced in a single cavity is desirable. The steps of subassembly, final assembly, as well as inspection, and conveying of the various components from location to location in and about the manufacturing area ar thereby eliminated. Prior art patents have disclosed various attempts to accomplish this.
U.S. patent application Ser. No. 615,603 filed in the name of Ernest F. Kiraly, et al. on May 31, 1984 describes a razor with a blade having a slot. According to the application the blade is permanently secured in the head portion of the razor and the handle and guard portion are molded integrally with the head.
British Patent 1,565,296 discloses making a unitary handle guard member and blade support and then attaching a z-shaped blade by upset rivets or the like to the support.
U.S. Pat. No. 4,489,626 issued Dec. 27, 1984 to Lembke describes a razor manufacturing process in which a double edged strip of blade metal is parted along a center line and cropped to form two strips, each containing a series of spaced apart blades connected by webs to an elongate backing strip. The strip of razors must be modified before subjecting it to molding thermoplastic material around the blades. Each modified strip, which then consists of a plurality of blades and a backing strip, is fed into a molding machine in which either the shaving unit or blade-containing-component of a razor is molded directly around each individual blade. The web is then parted to release the molded razor, etc. from the backing strip. It is unclear, according to Lembke, how the remaining razor components are manufactured. It is apparent, however, that the molding process relies, in part, on the blade being supported by metal connecting elements, e.g., webs 18, 24, et al. Lembke, therefore, requires the handling of an elongated metal strip, its control and insertion in either a multi-cavity mold or a single cavity mold, and in either case a sequential step of separating heads joined together in a single strip. Conveyance of a metal web of the type described is extremely difficult when it is necessary to protect a delicate cutting edge and even more so when two cutting edges must be protected. Moreover, a subsequent operation of separating the molded razor heads from the continuous strip must be performed. Thus, the Lembke process cannot be used to effect insert molding of an independent single or twin blade unit while maintaining a desired blade geometry, especially in a high speed process which will accommodate unit production in conjunction with existing razor blade manufacturing lines. Moreover, the need to control the elongated metal strip in the Lembke technology makes it unattractive for manufacturing, and it is not presently conceivable how the Lembke procedure could be adapted to producing twin blade products.
Other patents disclosing molding a plastic razor head around a blade are U.S. Pat. No. 3,070,883 (Grathwohl); U.S. Pat. No. 2,789,246 (Algier, et al.); and U.S. Pat. No. 3,703,765 (Perez).
Co-pending patent application Ser. No. 042,493 filed Apr. 24, 1987 describes the concept of forming a center mandrel of thermoplastic material and utilizing the combination of the blade and the center mandrel as a template-male mold member for subsequent molding of a compatible cap and blade support. This was a first attempt to overcome the problems associated with blade unit assembly and resulting inconsistency in blade performance. Although the technology reported and claimed in this first predecessor application indeed improved the wet-shaving assembly product, there still existed a need to eliminate an additional process step and further stabilize blade contour and performance.
In continuation-in-part application, Ser. No. 088,368 filed Aug. 27, 1987, an improved process was set forth which includes 1) supporting the blade with the mold by "butting" it against a forked member and clamping the blade at notches along each side, 2) forming the unitary blade support means and covering means by introducing thermoplastic material into the mold, and 3) mating the unitary means with a handle. Once again, improvement was achieved in product and process, but in order to successfully manufacture high quality units consistently at a commercially attractive production rate, the inventors continued to refine the concept of maximum blade stability in a single (or minimal) step process. Thus, continuation-in-part application, Ser. No. 165,859 filed Mar. 9, 1988, included the feature of protecting the "exposed" cutting edge of the blade in the method claim, and continuation-in-part application, Ser. No. 236,969 filed Apr. 26, 1988, is directed to a method which includes 1) supporting the blade within the mold on a forked member, 2) forming a unitary blade support and covering means, and 3) mating the unitary means with a handle.
While each of the above disclosures sets forth related techniques and products therefrom which are directed toward reducing the steps required to manufacture high quality blade assemblies consistently at a commercially-acceptable production rate, they do not appear to have provided the ultimate guidelines for adapting current blade production technology to an efficient method for high volume manufacture of shave-assembly units.
The present invention overcomes the problems described above which are encountered in known procedures, and results in optimum production of consistently high quality blade assemblies.